BLDC motors are today widely used in automotive as well as non-automotive applications. As opposed to classic brushed DC Motors, a BLDC motor always needs to have driving electronics. The driving electronics provide a rotating electric field in the stator coils, by applying a switching sequence of driving waveforms to these stator coils. The rotor itself is built up with permanent magnets, which will follow the rotating magnetic field of the stator coils.
In order to synchronise the position of the rotor with the position of the rotating field generated by the stator coils, it is required that the driving electronics are aware of the rotor position. This knowledge about the rotor position allows the driving electronics to correctly switch between the driving waveforms.
The rotor position information might be provided by a sensing unit such as for instance a Hall effect sensor or a rotary encoder, or can be derived in a sensorless way out of the voltage/current information on the motor terminals, for instance by measuring the back-electromotive force (BEMF) voltage in the undriven coils. These latter implementations eliminate the need for separate position sensors, and are therefore often called sensorless controllers.
In the past, several methods and systems have been identified for controlling BLDC motors with as feedback mechanism the BEMF voltage. For instance, U.S. Pat. No. 8,461,789 describes the calculation of a time T in response to the determination or estimation of a back EMF zero crossing event for a phase. The time T is representative of the desired absolute maximum value of the phase current. Current samples are taken by the current sampling unit symmetrically centred around T, and the values of the samples are input into an error function to calculate an error function value. The calculated error function value is used for calculating an adjustment value for the phase angle of the driving voltage profile that will minimise the absolute value of the error function. It is a disadvantage of the method described that relatively high filtering and calculation efforts are required. Also RAM usage is high. Moreover, the system provides limited dynamics because of the high calculation efforts.
Hence there is room for improvement in systems and methods for controlling and monitoring BLDC motors, bypassing the disadvantages mentioned.